The basic premise of Silver's article is that House districts have been more polarized of late. That is to say, there are fewer swing districts. In addition, fewer districts are voting for one party for House and another for president.

The conclusion one might draw is that many legislators have little reason to play to the middle, and that's why Washington seems more partisan than it used to be.

Back in 1976, there were near 25 states that came within three points of the nationwide margin and well over 30 that were within five points of the nationwide vote. In 2012, it was eight states within three points of the nationwide margin and 10 within five points.

Both of these totals are lower than 2008 and indeed the lowest in the past 50 years. Heck, there were only 14 states out of 50 where the statewide margin came within 10 points of the nationwide margin! Any way you slice it, there are fewer swing states than there used to be.

This increased polarization has translated to the Senate makeup. After the 1992 elections, when Republicans won 43 seats, 49% of the Democratic caucus came from states that voted more Republican than the country as a whole, while about 28% of the Republican caucus came from states where Bill Clinton won by a greater margin than he did nationwide. After the 2012 elections, in which Republicans won a slightly higher 45 seats than 1992, only 25% of the Democratic caucus comes from states where Obama underperformed his national margin, and only 16% of the Republican caucus comes from states Obama won by a greater margin than he did nationally.

The question that arises is how this increased polarization impacts on the seemingly growing partisanship of Washington. One would expect that it would, given that elected officials care most about getting re-elected and without fear of losing re-election in the general they play to the base to avoid a primary challenge.

One way we can test this hypothesis is to look at roll call votes. The DW nominate score method puts legislators on a scale from -1 for most liberal to 1 for most conservative. The folks who maintain the system at Voteview have plotted both the House and the Senate over the past 130 years.

You would think that House Democrats may have become more liberal over the past 20 years, given that they are increasingly safe districts. In 1992, only 51% of the Democratic caucus came from seats that were five points or more Democratic than the nationwide presidential vote. In 2012, 88% of Democrats came from districts won by Obama by five points or more – a 37-point increase.

Interestingly, the scores don't indicate that House Democrats have really become any more liberal.

Photograph: Voteview

The average Democrat was a little north of -0.4 after the 1992 elections and right at -0.4 in the last congress. This percentage has been fairly constant for the past 20 years even when the Democrats won more swing and red districts when they won back the majority from 2007 to 2011.

There has, however, been an increase in partisanship in the house, and it truly is "asymmetrical". The Republican House caucus has been becoming more conservative every year since 1977, whether or not House Republicans are winning or losing elections. Republicans have climbed from 0.4 on the DW nominate scales after the 1992 elections to near 0.7 in the last congress. That type of charge towards polarization is historically unusual over data that stretches back 130 years.

The fact that it is House Republicans who have become more partisan is somewhat surprising given that the party caucus is representing only slightly more Republican territory than it did 20 years ago. The percentage of Republicans representing seats that went for the Republican presidential candidate by five or more points than nationwide only increased from 74% to 90% – a 16-point increase. That is far less than the 37-point increase that House Democrats, who aren't much more partisan than used to be, experienced during the same timeframe.

The Senate picture matches that of the House.

Photograph: Voteview

Senate Democrats, like their House counterparts, are hovering around that -0.4 score – as they were 20 years ago. This levelness comes despite the Democratic caucus going from being 50/50 in the percentage of Democratic senators from Democratic-leaning states versus Republican-leaning states to 75/25.

Republicans, on the other hand, have slowly and become more conservative in their roll call votes by moving from about 0.3 to 0.5 on the scale. You might expect this trend given Republicans are representing more Republican leaning states, but the magnitude is quite noticeable given that the average Democratic ideology during the same period didn't move under polarization.

Yet, in the Senate, these roll call votes don't tell the whole story. Much of the perception that the Senate is home to partisan gridlock is that many bills can't get an up-or-down vote. We can measure this inability by looking at cloture votes to end debate. One must get 60 votes for cloture. When cloture attempts go up, it means that increasingly 60, not 51, votes are needed to pass a bill. Cloture doesn't equal filibuster, but the two are correlated.

The number of cloture motions since the Democrats took over the Senate in 2007 is 391, an average of 130 per Senate. It would take the last six Senates combined before 2007, that is to say those from 1995 through 2007) to match this total. In the final Senate before the Republicans took over in 1995, there were 80 cloture motions.

It's not just that Republicans aren't allowing bills to be voted upon in an up-or-down vote, it's that they are blocking bills in far greater numbers than they did 20 years ago.

When Democrats were in the minority for of the 1995 to 2007 time period, the most cloture motions that were filed in a Senate was 82. Since 2007, the fewest number of clotures in a Senate has been 115. The average number per Senate when Democrats were in the minority was 70 – some 50 less than when Republicans were in the minority the past six years.

Yes, Democrats block bills, but Republicans block many more. This is gridlock at its finest (or worst).

When you put all these statistics together, the portrait painted becomes rather clear. Polarization is definitely up on the congressional district and state level. Yet, the feeling that Democrats and Republicans are further apart than they used to be is upon inspection of the evidence more because of Republicans than Democrats.